Typical examples of electronic material resins that are used as the resin component of photoresists used during the production of electronic devices such as semiconductor elements, liquid crystal elements and magnetic heads and the like include polyhydroxystyrene based resins (such as resins in which a portion of the hydroxyl groups are protected with acid dissociable, dissolution inhibiting groups, copolymers of hydroxystyrene units and styrene units, and copolymers of hydroxystyrene units and (meth)acrylate esters) in the case of KrF resist resins, and (meth)acrylate ester copolymer based resins in the case of ArF resist resins.
Examples of processes for refining these types of electronic material resins include the processes disclosed in the patent reference 1 listed below in the case of the former type polyhydroxystyrene based resins, and the processes disclosed in the patent reference 2 listed below in the case of the latter type (meth)acrylate ester copolymer based resins.
The patent reference 1 discloses a process in which the resin is dissolved in a polar solvent such as N-methylpyrrolidone and an aliphatic hydrocarbon based solvent, and following phase separation the resin is obtained from the polar solvent layer, as well as a process in which the resin is dissolved in a lower alcohol, and is then added to a poor solvent such as water to precipitate the polymer.
The patent reference 2 discloses a process in which the resin is refined using an aliphatic hydrocarbon such as n-hexane, or a mixed solvent of an aliphatic hydrocarbon and ethyl acetate.
Patent Reference 1: Japanese Unexamined Patent Application, First Publication No. Hei 6-289614
Patent Reference 2: Japanese Unexamined Patent Application, First Publication No. 2002-201232
However, when a crude resin for an electronic material containing structural units derived from a (meth)acrylate ester with a hydrophilic site such as a lactone is refined using these types of processes, even if the unreacted monomer is able to removed to some extent, the removal of materials of comparatively high polarity such as by-product oligomers or low molecular weight polymers is particularly difficult. Consequently, the use of resins containing these types of by-products that are difficult to remove as components of electronic materials is unavoidable.
For example, when an ArF chemically amplified photoresist composition is prepared using a resin containing by-products such as the oligomers and the like described above, although the various characteristics such as the sensitivity, the resolution, and the resist pattern shape are satisfactory, the number of defects (surface defects) in the resist pattern following developing can become problematic. These defects refer to general problems such as scum and bridging between resist patterns detected by inspecting the developed resist pattern from directly overhead using a surface defect observation apparatus manufactured by KLA Tencor Corporation (brand name “KLA”).
Furthermore, during storage as a resist solution (a photoresist composition in solution form), problems may also develop in terms of the storage stability as a resist solution, resulting in the development of fine particles in the solution. Moreover, if these fine particles develop, they can cause the type of defects described above, meaning improvements in the storage stability as a resist solution are needed in order to improve the level of defects.